1. Field of the Invention
The present invention relates to a mounted structure of printed circuit board in a semiconductor package and more particularly to a mounted structure of printed circuit board (PCB) in a semiconductor package adapted to allow flux gas to be easily discharged outside to thereby prevent generation of void.
2. Description of the Prior Art
Generally, semiconductor manufacturers are accelerating development of new types of packages and trying to apply same to the manufacture of semiconductors according to the current trend of miniaturization and high functionalism of electronic parts.
By way of example, an existing representative type of package, Quad Flat Package (QFT) is being rapidly replaced by new types of packages such as Ball Grid Array (BGA), flip chip, Chip Size Package (CSP) and the like. However, the new types of packages have raised problems in that the packages cannot be soldered onto PCB unless a new technique of printing a cream solder is supported, specifically, in case of CSP.
Furthermore, a technical field for designing a solder resist is also important in addition to the cream solder thus mentioned. There is a problem in the conventional design of solder resist in that a large quantity of voids are generated at a soldering part to thereby decrease reliability of PCB mounted with a package.
FIGS. 1 and 2 are schematic diagrams for illustrating a mounted state of a Chip Size Package, 1 of Land Grid Array type to a PCB 2, where, the PCB 2 formed with a solder resist 3 is printed with a cream solder 4, and then, a substrate 5 mounted with the CSP 1 formed with the solder resist 3 is positioned on the PCB 2 to perform a reflow soldering and to mount the CSP 1 to the PCB 2.
At this time, in case a copper pad 6 formed underneath the substrate 5 of the CSP 1 is thicker than the solder resist 3, the solder resist 3 of PCB 2 contacts the solder resist 3 formed underneath the substrate of the CSP 1 to create a hermetic void such that flux gas cannot be extracted, thereby, generating a void therein.
When the flux gas is kept inside, the soldering part, the flux gas in captivity in the void absorbs heat and in the processes of contraction and expansion, cracks are generated in the soldering part, leading to a functional paralysis of the PCB 2.
In order to overcome the generation of the void, holes are conventionally drilled to the PCB to leak out the flux gas, however, there is a problem in the conventional method thus described in that it is next impossible to drill a PCB due to the current trend of miniaturization of electronic parts.